Along with the popularization of cameras, real-time monitoring with a camera becomes more and more popular. A camera may acquire an image in a monitoring area during real-time monitoring, while there may usually exist a sensitive area, such as a vicinity of a socket, a door and a window and the like. In the monitoring area of the camera, an unsafe event may occur when a specific object is located in the sensitive area, for example, it may be dangerous when a child is located nearby the socket, so that there is an urgent need for an alarming method which may prevent occurrence of an unsafe event.